Translating devices have traditionally been used in many ways including the movement of control elements. These devices are required to be mounted on a rigid support to withstand the axial loading of both the driving mechanism and the control element. Examples of applications include the positioning of loads for manufacture, control rods in nuclear reactors, and graphite electrodes in electric arc furnaces.
Rotational movement of translational devices has been obtained by mounting the device in a gimbal, which permits the device to be located at an infinite number of positions with a similar complexity in specifying the exact location and controlling the movement. Gimbals plus translational drives have been used to change the position of water cooled plasma torches in plasma torch melters. The relatively high temperature and large diameter of graphite electrodes used in plasma arc melters has apparently precluded a similar use. In addition, the graphite-electrode arc melter has usually been used for metal melting or smelting which have good heat conduction to the edges of the melt and have not required lateral movement of the ends of the electrodes. With the processing of more nonmetallic materials in the thermal treatment of hazardous and radioactive waste, the need to manipulate the graphite electrodes is more important because of the lower heat conductivity and lower fluidity of the molten slag or glass at similar temperatures. The capability to move the electrodes laterally is very desirable in this case. For waste processing applications using plasma arc melters, the melter size is compact and the relatively large feed ports and offgas exhaust ports limit space available for the electrode or torch cooling and three-dimensional drive mechanisms. As a result, a simple, compact mechanism for moving the electrode or torch tip both laterally and longitudinally was needed.
The most common way to position a control element, required to be located on an axis other than the main translating axis, is achieved by means of a gimbal. In a melter, this requires a machining of an element which matches a socket in the mounting.
Nuclear reactors use a penetration, tilted to the reactor vessel and core, to locate a control rod in a position not parallel to the vessel axis. This application is not adjustable for different radial positions.
Electric arc furnaces generally use axially translating electrodes mounted vertically in the furnace head. (This application is also not adjustable for different radial positions.)
These furnaces use an electrode positioning device based on a pulley and cable or hydraulic power to position a clamp device on a mast vertically. The electrode is affixed in a clamp attached to the mast to which is attached the bus tubes for power attachment.